The teachings herein relate generally to techniques for rapid detection of phase and amplitude information in an electrical signal.
Present state of the art assumes a steady voltage and a steady frequency as important references for the orientation of responses. Often a single set of frequencies and amplitudes are insufficient to describe the true nature of the signal, and severely limit the responses of the system. Furthermore, if other knowable frequencies and magnitudes are not eliminated from the response, then substantial control effort is misdirected.
In the case of power converters, the present state of the art uses phase-lock loop circuits to identify single frequencies and single magnitudes. This approach without the present invention does not remove the unwanted amplitude and frequency responses, and cannot be directed singularly to the desired response.
In the case of highly-reliable, cost-sensitive power conversion equipment, as might be used in wind turbines, the present invention directs more of the control effort to the useful response of the power-limited elements.
Many countries now require that electric power generation facilities stay connected with the electric grid when the grid is faulted. Additional requirements include the ability to control real and reactive power flow during a voltage depression created by a grid fault, and the ability to recover quickly following fault clearing. The ability of the generator to meet these requirements is heavily dependent on the design of the converter control system to track the phase and amplitude information of the sequence components at the point of connection with the grid. Accurate and rapid tracking capability is necessary for the control systems to make timely adjustments to the converter thereby mitigating the effect of any large signal transients created by grid faults or other grid disturbances.
Detection of the fundamental frequency phase and amplitude information during grid faults is difficult because of the distorted and unbalanced components in the measured grid signals. Previous efforts to address the distorted and unbalanced components are too slow and limit the performance of the control system. Such is the case for conventional phase-lock-loop (PLL) design. Efforts involving conventional PLL have typically been designed with relatively slow response in order to accommodate the distorted and unbalanced input voltage. Thus, even under a symmetrical fault, the response of PLL systems is not as rapid as desired. Accordingly, the need for rapid detection of system information presents a critical challenge to PLL design.
This invention will describe a technique for rapidly detecting the desired components of a distorted and unbalanced signal having a plurality of sequence components of different frequencies.